In order to achieve climate targets, so-called negative emissions are discussed in numerous scenarios and strategies. Negative emissions are defined as the removal of carbon dioxide (CO2) from the atmosphere and its long-term storage. One possible technology is the direct removal of CO2 from the air. This is called Direct Air Capture (DAC), or Direct Air Carbon Capture and Storage (DACCS) in the case of subsequent storage.

In their article, Simon Block and PD Dr. Peter Viebahn from the Sectors and Technologies Research Unit at the Wuppertal Institute and Prof. Dr. Christian Jungbluth from the NOWUM-Energy Institute at Aachen University of Applied Sciences analyse the use of a "low-temperature" DAC process in several case studies for northern, central and southern Germany. In particular, they considered the consumption of resources (energy, water and land) and the costs that would be required to extract and store 20 megatonnes of CO2 per year. They identified that generating the large amounts of electricity and heat required for the use of DAC in particular leads to high land requirements. Around 46 per cent of the electrical energy requirement is therefore due to the operation of air-source heat pumps using electricity from photovoltaics or wind power to meet the heat requirements of the DAC process. Overall, DAC systems would account for 1.4 per cent of Germany's total electricity demand in 2045.
For this reason, and due to the low DAC temperature level of 100 degrees Celsius, the authors see the use of existing waste heat in particular as an opportunity to reduce electrical energy demand. However, the investment costs for the DAC system in particular account for more than 60 per cent of the specific CO2 removal costs.
The authors calculated specific costs of 125 to 138 euros per tonne of CO2 removed. If the transport and storage of the CO2 in geological reservoirs under the North Sea is taken into account, the costs increase to 161 to 176 euros per tonne of CO2. This is roughly in line with the projected price of 160 euros per tonne of CO2 in the European Union's emissions trading system for 2030.

However, as there are only a few small DAC plants worldwide, all assumptions and the resulting results are subject to a high degree of uncertainty. The authors therefore point to the need for further research and outline a research programme for DAC, which should in particular highlight the implications for the energy system and provide a holistic assessment of future implementation in Germany.

The article was written as part of the project "iNEW 2.0 – Incubator Sustainable Electrochemical Value Chains" and is available (Open Access) via the linke below.